You can judge the quality of their faith from the way they behave. Discipline is an index to doctrine.
TertullianHe has inhibited discussion by designating admonition as the method of dealing with a heretic- and the first method, too, because he is not a Christian. This is so that he would not seem to require correction again and again and before two or three witnesses as though he were a Christian. He ought to be corrected for the very reason that he is not to be disputed with. In addition, this is said because a controversy over the Scriptures can, clearly, produce no other effect than help to upset either the stomach or the brain.
Tertullian